Well drilling operations in subterranean formations, such as those directed to producing oil, typically require circulating a drilling fluid (i.e., mud) through a drilling fluid circulation system. The circulation system may include a drilling rig for supporting lengths of drill pipe (“drillstring”) that are fastened to a drill bit and a mud pump. During drilling operations, the drilling fluid may be pumped by the mud pump through the interior of the drillstring, through the drill bit, and returned to the surface through the annulus (i.e., the area between the outside of the drill pipe and the well wall). The drilling fluid cools the drill bit and cakes the sides of the well helping to keep the well from caving in until steep pipe or cement is put in place when the well is completed. Moreover, the weight of the drilling fluid prevents any oil, gas, or water in the subterranean formation from gushing out through the well to the surface.
One of the primary functions of the drilling fluid is to carry “cuttings” (e.g., rock chips or gravel) generated by the drill bit back to the surface so that the hole or wellbore is cleaned efficiently. However, when drilling deviated (i.e., greater than 30 degrees) and extended reach wells, the drilling fluid is ineffective in carrying away drilled cuttings which tend to accumulate in the lower side of the annulus. These accumulated cuttings may eventually form a temporary or permanent “cuttings bed” resulting in pipe sticking, as well as increased torque and drag on the drillstring. Furthermore, failure to clean the accumulated cuttings may lead to formation hole fill-ups, fractured formations, decreased drill bit life, slower rate of penetration, and an increase in the annular density of the hole. Moreover, the cuttings concentration in these wells causes additional annulus equivalent circulating density (“ECD”) which may result in a loss of fluid flow up the annulus due to changes in hydrostatic pressure.
One previous solution to the above-described problems required rotating the drillstring while drilling deviated holes to influence cuttings transport, so that the cuttings are dispersed into the higher fluid velocity region of the hole by the mechanical stirring action of the drillstring. However, drillstring rotation has been proven to be ineffective at cleaning accumulated cuttings which have formed a permanent cuttings or “dead” bed in the deviated hole. In order to solve this problem special “downhole” cleaning tools have been developed which are attached to the drillstring during drilling. These downhole cleaning tools typically have fixed external blades and use the rotation and/or reciprocation (i.e., alternatively raising and lowering) of the drillstring so that the fixed blades assist in the removal of dead bed cuttings from the wellbore. These downhole cleaning tools, however, are useless in non-accumulating cuttings areas (i.e., outside of the dead bed) as the fixed blades unnecessarily increase the torque and drag on the drillstring thus reducing the circulation of the drilling fluid and consequently overall cleaning effectiveness in these non-accumulating areas.
It is with respect to these considerations and others that the present invention has been made.